Conventional coffee-making machines commonly used in offices, restaurants and coffee shops are provided with a water reservoir, a heating element in the reservoir and various heat and flow controls so that an appropriate quantity of hot water is available for coffee brewing purposes. The ground coffee is contained in a removable filter unit disposed below a sprayhead in fluid communication with the hot water reservoir. When it is desired to brew a pot of coffee, hot water from the reservoir is delivered to the sprayhead and then onto the ground coffee contained in the filter unit.
Most coffee-making machines of this nature have a single valve, which controls the amount of water delivered from the hot water reservoir to the sprayhead. For example, U.S. Pat. No. 5,063,836 to Patel, assigned to the assignee of the present invention, discloses a coffee-making machine having a single valve controlling the flow of hot water from the hot water reservoir to the sprayhead. The duration of time the valve remains open is regulated by a timer. The valve is kept open longer when larger amounts of coffee are to be brewed. Therefore, depending on the amount of coffee to be brewed, the coffee grounds are exposed to hot water from the sprayhead for different durations. It has been found that exposing coffee grounds to hot water for different durations sometimes yields inconsistent coffee.
Still other types of coffee-making machines have employed a bypass method for delivering varying amounts of water onto the coffee grounds. Depending on the amount of coffee to be brewed, some of the water exiting the hot water reservoir bypasses the coffee grounds to avoid contact therewith. While this maintains the water contact time with the coffee grounds generally constant for different amounts of brewed coffee, not all of the water exiting the hot water reservoir contacts the coffee grounds. As a result, uneven extraction of the coffee grounds occurs leading again to a varying quality of brewed coffee.
It is therefore an object of the present invention to provide a novel coffee-making machine, which obviates or mitigates the above-identified disadvantage.